The present invention relates to a method for controlling accessories of a motor vehicle, which act via a loss torque on the drivetrain of the motor vehicle.
Currently, vehicles are equipped, in regard to comfort and security, with ever more and/or ever larger accessories (a.k.a., secondary assemblies) such as the air-conditioning system (air-conditioning compressor), generator, power steering pumps, pumps for chassis stabilization, or the like. All of the secondary assemblies act indirectly or directly as producers of loss torques acting on the drivetrain, in that, because of their operation, in addition to the pure engine drive torque to be applied by the drive unit (e.g., internal combustion engine and/or electric motor) to accelerate the motor vehicle or solely to maintain idle operation without activated secondary assemblies, they load the drive unit with additional torque to be produced (so-called loss torque) for their own operation. In particular, in lower-power motors, the problem thus arises that the drive unit may not meet (or provide) the particular demanded total torque in every operating state. In this meaning, the torque converter of an automatic transmission also acts as a secondary assembly generating a loss torque.
The present invention is based on the object of specifying a method for controlling secondary assemblies of a motor vehicle, which act on the drivetrain of the motor vehicle via a loss torque, which ensures operation of the drive unit in conformity with demand in all operating states of the drive unit, and in particular prevents startup weakening or undesired snapping off (stopping) of the drive unit during idle operation.
The object is achieved according to the present invention by a method for controlling secondary assemblies of a motor vehicle including at least one deactivatable secondary assembly which generates a loss torque. By ascertaining and subsequently monitoring a total loss torque to be expected and possibly deactivating a deactivatable secondary assembly as a function of the monitoring result, secure operation of the drive unit in conformance with demand is ensured in every operating state. To ascertain the fictive total loss torque to be expected, the deactivation dead time (required time which passes from the instant of the deactivation command until the actual beginning of the deactivation procedure) of at least one deactivatable secondary assembly which generates a loss torque (referred to below as a deactivatable secondary assembly) is ascertained. If multiple deactivatable secondary assemblies are provided, at least the shortest deactivation dead time is ascertained. The deactivation dead time may be read out from a stored table of the deactivation dead times for all deactivatable secondary assemblies or from a memory area in the deactivatable secondary assembly itself.
Starting from the currently existing total loss torque (sum of the currently applied loss torques of all (active) secondary assemblies), it is then ascertained what fictive total loss torque (current total loss torque+loss torque of all (active) secondary assemblies after passage of the deactivation dead time of a secondary assembly potentially to be deactivated) would result after passage of the deactivation dead time used as a basis. The fictive total loss torque is estimated, for example, by calculating which torque may be absorbed at most by all participating secondary assemblies upon passage of the deactivation dead time. For this purpose, the currently absorbed torque, the maximum absorbable torque, and the maximum torque gradient are advantageously ascertained for every (active) secondary assembly. Finally, the ascertained total loss torque to be expected is compared to a predefined torque threshold (monitoring) and if the threshold is reached or exceeded, the secondary assembly whose deactivation dead time was used for ascertaining the loss torques of all secondary assemblies is deactivated (shut down).
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.